A ferrite antenna comprises an elongated coil wound on a rod of ferrite or powdered-iron material and tuned with a series or parallel capacitor so as to be resonant at the operating frequency. The ferrite core increases the radio-frequency flux in the coil and also permits the necessary inductance to be obtained with relatively few turns of wire. In this way, the resistance is kept low and the coil Q is maintained at a high value, much higher than that of an air-wound coil of the same size.
Ferrite antennas of this type are often used in portable communication systems such as those employed in underground mines where the inductive field produced by the antenna is coupled to nearby conductors which carry the signal to a remote location where it is detected. One difficulty with such antennas, however, is that they generate a magnetic moment field which circulates very close to the axis of the antenna. As a result, difficulty is encountered in having the field reach nearby conductors to induce the current flow necessary to sustain near-field communication over long distances as is required in the mining industry.